10 KiB
[comparisons]
22 General utilities library [utilities]
22.10 Function objects [function.objects]
22.10.8 Comparisons [comparisons]
22.10.8.1 General [comparisons.general]
The library provides basic function object classes for all of the comparison operators in the language ([expr.rel], [expr.eq]).
For templates less, greater, less_equal, andgreater_equal, the specializations for any pointer type yield a result consistent with the implementation-defined strict total order over pointers ([defns.order.ptr]).
[Note 1:
If a < b is well-defined for pointers a and b of type P, then (a < b) == less
()(a, b),(a > b) == greater
()(a, b), and so forth.
â end note]
For template specializations less, greater,less_equal, and greater_equal, if the call operator calls a built-in operator comparing pointers, the call operator yields a result consistent with the implementation-defined strict total order over pointers.
22.10.8.2 Class template equal_to [comparisons.equal.to]
template<class T = void> struct equal_to { constexpr bool operator()(const T& x, const T& y) const; };
constexpr bool operator()(const T& x, const T& y) const;
Returns: x == y.
`template<> struct equal_to { template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward(t) == std::forward(u));
using is_transparent = unspecified; }; `
template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) == std::forward<U>(u));
Returns: std::forward(t) == std::forward(u).
22.10.8.3 Class template not_equal_to [comparisons.not.equal.to]
template<class T = void> struct not_equal_to { constexpr bool operator()(const T& x, const T& y) const; };
constexpr bool operator()(const T& x, const T& y) const;
Returns: x != y.
`template<> struct not_equal_to { template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward(t) != std::forward(u));
using is_transparent = unspecified; }; `
template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) != std::forward<U>(u));
Returns: std::forward(t) != std::forward(u).
22.10.8.4 Class template greater [comparisons.greater]
template<class T = void> struct greater { constexpr bool operator()(const T& x, const T& y) const; };
constexpr bool operator()(const T& x, const T& y) const;
Returns: x > y.
`template<> struct greater { template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward(t) > std::forward(u));
using is_transparent = unspecified; }; `
template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) > std::forward<U>(u));
Returns: std::forward(t) > std::forward(u).
22.10.8.5 Class template less [comparisons.less]
template<class T = void> struct less { constexpr bool operator()(const T& x, const T& y) const; };
constexpr bool operator()(const T& x, const T& y) const;
Returns: x < y.
`template<> struct less { template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward(t) < std::forward(u));
using is_transparent = unspecified; }; `
template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) < std::forward<U>(u));
Returns: std::forward(t) < std::forward(u).
22.10.8.6 Class template greater_equal [comparisons.greater.equal]
template<class T = void> struct greater_equal { constexpr bool operator()(const T& x, const T& y) const; };
constexpr bool operator()(const T& x, const T& y) const;
Returns: x >= y.
`template<> struct greater_equal { template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward(t) >= std::forward(u));
using is_transparent = unspecified; }; `
template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) >= std::forward<U>(u));
Returns: std::forward(t) >= std::forward(u).
22.10.8.7 Class template less_equal [comparisons.less.equal]
template<class T = void> struct less_equal { constexpr bool operator()(const T& x, const T& y) const; };
constexpr bool operator()(const T& x, const T& y) const;
Returns: x <= y.
`template<> struct less_equal { template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward(t) <= std::forward(u));
using is_transparent = unspecified; }; `
template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) <= std::forward<U>(u));
Returns: std::forward(t) <= std::forward(u).
22.10.8.8 Class compare_three_way [comparisons.three.way]
namespace std {struct compare_three_way {template<class T, class U>constexpr auto operator()(T&& t, U&& u) const; using is_transparent = unspecified; };}
template<class T, class U> constexpr auto operator()(T&& t, U&& u) const;
Constraints: T and U satisfy three_way_comparable_with.
Preconditions: If the expression std::forward(t) <=> std::forward(u) results in a call to a built-in operator <=> comparing pointers of type P, the conversion sequences from both T and U to P are equality-preserving ([concepts.equality]); otherwise, T and U model three_way_comparable_with.
Effects:
If the expression std::forward(t) <=> std::forward(u) results in a call to a built-in operator <=> comparing pointers of type P, returns strong_ordering::less if (the converted value of) t precedes u in the implementation-defined strict total order over pointers ([defns.order.ptr]), strong_ordering::greater if u precedes t, and otherwise strong_ordering::equal.
Otherwise, equivalent to: return std::forward(t) <=> std::forward(u);